The thing is, the way a spin class is run is counter to how you actually ride. On the road you change gears to keep the "resistance" the same and maintain your highest efficiency cadence. I hate classes that spend too much time in low cadence or out of the saddle situations. It's fine for building strength, but doesn't translate to the actual road. I'd never climb a hill on the road in a hard gear at 60 cadence if I could lower the gear, maintain 80-90 and keep the same speed... and at the same time use less energy.